As a general statement, mTORs are cellular regulatory proteins essential for the activation of proteins specific or important to growth and cellular replication. Almost any factor important to protein synthesis affects mTOR activation to some degree by interacting with the TSC1/TSC2 protein complex. Relevant to the question, the underlying mechanisms for many tumors and cancers involve dysregulation of mTOR cell signaling pathways (usually an abnormal up-regulation of mTOR components). Thus, as an approach to controlling the growth of cancerous cell lines, the use of mTOR inhibitors has been proposed. The question or concern related to PQQ evolves from such observations, specifically the report by Kumar et al. in Anticancer Agents Med Chem. 2015;15:1297-304 (https://www.ncbi.nlm.nih.gov/pubmed/25832358). These researchers observed that PQQ exposure lessens the growth of human leukemia HL-60 Cells through Inhibition of mTOR. Thus the question – Could something similar happen in muscle?

The cells in question versus muscle cells:

HL-60 (Human promyelocytic leukemia) cells are derived from a type of blood cells, known as neutrophils. HL-60 cells proliferate continuously in suspension cell cultures. Accordingly, they are used in cell proliferation studies or studies in which cells with the characteristics of phagocytic cells, such as neutrophils, are the focus of an investigation. Phagocytic cells are cells that are recruited to the sites of infection, cell injury, and inflammation. An interesting observation is that when activated, some of their mitochondrial content gets extruded (cf. http://www.tandfonline.com/doi/full/10.1080/15548627.2015.1063765) in to plasma/blood. In this regard, plasma levels of mitochondrial DNA (from phagocytic and the targeted damaged cells) can be used as a marker for the extent of inflammation in human and animal subjects. Phagocytic cells can even generate hydrogen peroxide and superoxide radicals to aid in the chemical modification of inflammatory by-products and cellular debris.

Muscle cells, of course, are different. In vivo, they do not replicate or “turn-over” rapidly, in contrast to phagocytic cell lines. Their mitochondria stay intake and are not extruded. Oxygen utilization is efficient and used for ATP production, which in part is in contrast with phagocytic cells, wherein some of the cellular oxygen is directed at “oxidant” and superoxide production. The point here is that interpretation of results related to cell signaling is cell-type and process dependent. When the only data available are derived from cells in culture, it ‘s hard to make assertive conclusions without a lot of nuance and other assumptions.

mTOR, PQQ, and Muscle

So – can mTOR levels influence muscle growth. The answer in some situations is yes. Several research groups have noted that there is a sarcopenic effect (presence of lower muscle mass and either lower muscular strength or lower physical performance) with long-term mTOR inhibitor use (e.g. for long-term cancer treatment. (cf. Gyawali et al. Muscle wasting associated with the long-term use of mTOR inhibitors. Mol Clin Oncol. 2016; 5:641-646). Importantly, only very very potent mTOR inhibitory agents have been studied. Thus, to what extent this has a direct relevance to a normal exercising person taking PQQ is not clear. Moreover, as it relates to PQQ, there are few comparative studies of using differing cells and their response to PQQ exposure. We know of only one. Min et al. reported (J Cancer. 2014; 5:609-24, https://www.ncbi.nlm.nih.gov/pubmed/25161699)

PQQ exposure enhanced apoptosis (programmed cell death) in tumor cells (3 types of tumor cells were studied) but promoted no apoptotic changes in the normal cell lines derived from renal and umbilical-derived cells. Accordingly, an answer to the PQQ/muscle question is, if there is an effect, it is probably modest, if at all. Importantly, exercise “trumps” most known dietary factors and nutraceuticals taken as supplements to optimize muscular function or maintenance.

As a final comment, for questions such as the one posed, going to the resveratrol literature is sometimes helpful. In many respects PQQ and resveratrol (RV) influence similar cell signaling pathways. A PubMed search identified over 50 papers addressing RV, tumor growth, and apoptosis, i.e. RV suppresses tumor growth. In contrast, there are dozens of paper suggesting RV improves many aspects of muscle function. For PQQ, although the literature is not as extensive, the available reports suggest similar findings.

Summary

In an active individual, is PQQ going to do much independent of the effects of exercise? Few external factors promote muscular or mitochondrial function as well as exercise itself. The mTOR cell signaling pathways are clearly essential to muscle function, but any mTOR inhibitory response that PQQ might have is probably overridden by other factors. For example, PQQ has been shown in animal studies to have clear positive effects on neonatal growth, anti-ischemic/cardio-protective effects, neural protective effects, an ability to enhance fatty acid metabolism via mitochondrial oxidation, and anti-inflammatory effects. Rather, than increasing performance per se, the benefits of PQQ, if any, are more likely related to recovery following an episode of intense activity. In this regard, some mTOR suppression may have some utility.

The answer is that it probably makes little difference, if prudent. The amounts of pyrroloquinoline quinone and its derivatives in the diet are in the milligram range, if that. Most PQQ supplements that are currently sold range in amounts from 5-20 mg to be taken on a daily basis.

On the positive side – PQQ is an activator of the sirtuin family of proteins and other factors important to cell cycling and repair, which seem important to renal protection. For example, these factors when poorly activated may contribute to metabolic kidney disease, such as that this is associated with diabetic nephropathy.

On the potentially negative side is that many so-called antioxidants (PQQ included) under some conditions may act as “pro-oxidants”, particularly at high concentrations. In an acute study using rodents, nephrotoxicity was observed after 3-4 days when rats were given doses above 10 mg per day by intra-peritoneal injection (Hiroshima J Med Sci. 1989; 38:49-51). The most prominent finding was necrotic and degenerative changes of the proximal tubular epithelium of the kidney. As a direct comparison, that would be the equivalent of being injected with 2.0 to 2.5 grams of PQQ on a daily basis or even after various metabolic based corrections, 200-250 mg of PQQ (e.g., a person weighing about 150 pounds). For further perspective, many common vitamins are toxic at this level too, when administered by injection.

In another study, rats were given doses of 0, 100, 200 and 400 mg/kg body weight per day by gavage (the administration of food through a tube into the stomach) for 13 weeks. However, in this case NO toxicologically significant changes were observed based on what was described as “thorough pathological and toxicological examinations”. It is important to mention here that pyrroloquinoline quinone taken orally is subject to a broader range of metabolic modifications, than when injected directly.

Summary: PQQ supplements seem safe when taken orally (e.g. even at 10-20 mg doses daily) by those with normal kidney function. In animal models with kidney disease, PQQ seems to provide some protection for metabolic-related kidney disease. However, there are no human studies that address this point nor studies that speak to kidney diseases of more genetic-based origins, such as polycystic renal disease. To be prudent, as you would be with any substance taken in substantial quantities when there is also qualifiers, such as evidence of renal or liver disease, please consult your physician before making dietary changes.

Several readers have inquired about PQQ in food and whether diet alone is sufficient to obtain enough pyrroloquinoline quinone to be biologically effective. The answer — relative to what is known about optimizing growth in rodent nutritional growth experimental models — is probably yes. However, some rather broad assumptions have to be made, because of the limited amount of data regarding the forms of PQQ in different foods.

Natto and green tea are high in PQQ

For perspective, Dr. Steinberg out of the University of California, Davis has presented data that suggests PQQ is needed at ~200-400 micrograms per kilogram of dry food. Given that most lactating mammals have the same vitamin and mineral requirements, when those amounts are expressed on a food energy or dry food weight basis, one might infer humans — who consume about 300 to 500 grams of dry food per day (about 2000 Kcal) — need up to 100-200 micrograms of PQQ per day.

PQQ in Food *

* In addition to the values taken from published papers, some of the values are from conference reports or abstracts presented at meetings. As noted in the main body copy, there is a lot of variability. Kamazama et al. in their 1995 Biochemistry Journal paper report ~0.06 micrograms as the PQQ concentration in dried skim milk per 100 grams of milk solids. However, later in an abstract of a paper presented at the Biochemical Society Transactions in 2000 in England, they report detection and quantization of IPQ in human breast milk at 0.14 to 5.5 microgram/100 mL of fresh milk or 1.4 to 55 micrograms per 100 grams of milk solids. Given the variability, my estimates are inline with the data reported in Characterization of Pyrroloquinoline Quinone Amino Acid Derivatives by Electrospray Ionization Mass Spectrometry and Detection in Human Milk, i.e. ~140-180 micrograms (PQQ +IPQ) per 100 g of milk solids. Moreover, Fluckinger et al. reported that the PQQ concentration of milk is 15-150 micrograms/100 mL or 150 to 500 micrograms/100 grams of bovine milk solids. For the Fluckinger assays PQQ was separated and then measured using a 16-channel electrochemical detector, a highly precise and sensitive procedure. All other assay involved sophisticated separation and mass spectrometer for detection, also highly precise and sensitive. The information above is also derived from the work of Kumazawa et al. (Levels of pyrroloquinoline quinone in various foods). Some of the values are higher than corresponding values for foods analyzed by Noji et al. (Simple and Sensitive Method for Pyrroloquinoline Quinone (PQQ) Analysis in Various Foods Using Liquid Chromatography/Electrospray-Ionization Tandem Mass Spectrometry). Although the number of foods analyzed is small, an important finding is that PQQ has been observed in all tissues analyzed to date in both plants and animals.

In the above table, Column A indicates some of the currently available sources for pyrroloquinoline quinone (for which compositional values have been obtained). Column B are amounts taken mostly from the Kumazawa et al. paper, but are expressed as micrograms of PQQ per 100 grams of food (~1/4 lb) and not as nanograms per grams of food (as they were originally reported). Next, in column C, the amounts in column B are multiplied by 5-10 to obtain an estimate of micrograms of PQQ per 100 grams of dried foods or so-called food solids (e.g., given that most of the food items mentioned contain at least 75% water or more). Column D requires making some guesses. As noted, some researchers have reported that IPQ is 5 to 8 times greater than the amount of PQQ in tissues. While others have reported a low ratio of 2 to 3 for IPQ to PQQ. Thus, the apparent IPQ + PQQ values given in Column D range from the lowest to highest amounts obtained by multiplying arbitrarily the values in Column C by 2 or 8. Column E is even trickier. It represents the estimated amounts consumed per day for an “ideal” person consuming a maintenance diet of 2000 calories per day. Regarding the diet consumed, the values for the major food categories are based on the estimated amounts consumed per day (on a dry weight basis) derived from values given in the USDA publication, Profiling Food Consumption in America. The question is whether a typical selection of food can yield the minimum amount that corresponds to optimizing growth in animal models, i.e. about 100-200 microgram per day.

Regarding various conclusions, the first is that much better data is needed. However, setting aside that concern and assuming the actual values for PQQ in foods may be at the median (middle) of the estimates provided, one can guess that a typical intake in humans is indeed about 0.3 mg or 300 micrograms of pyrroloquinoline quinone per day or more. That amount is very much is line with the amount of pyrroloquinoline quinone or PQQ + IPQ needed to stimulate growth in animals. It is also an amount that is found in human milk, which is always a good starting point in assessing a need related to growth or maintenance.

So what can we conclude? In the paper by Kumazawa et al. Levels of pyrroloquinoline quinone in various foods it is stated that probably the PQQ in animal tissues are derived at least in part from their diet and that the levels of pyrroloquinoline quinone in plant tissues are in the aggregate about 10 times those in animal tissues. In a review by Rucker et al. Potential physiological importance of pyrroloquinoline quinone, the same conclusion was reached, particularly given that stomach microflora does not make an abundance of PQQ . The data also beg the question do we need supplements and if so how much? Many of the PQQ products sold are in the 10-20 mg range. As indicated in the section — PQQ Dosage, What size pyrroloquinoline quinone pills should I take? — we discuss that the reasonable pyrroloquinoline quinone dosage, like many supplements, for an active adult is probably the result of an arbitrary decision.

As a final point, unlike many dietary factors and biofactors, PQQ and its derivatives are sustained in tissues and seem to play a fundamental role related to energy metabolism. In this regard, the need for PQQ might vary depending on your desired outcome.

Searching for PQQ information?

If you are the type of person that concerns themselves with optimal nutrition, you probably have noticed that a few forward thinking nutritional companies have added some sort of PQQ supplement to their line of products. Pyrroloquinoline quinone is quickly gaining in popularity as a potent antioxidant, rivaling both resveratrol and quercetin as the most beneficial nutraceutical of the three.

So what do we know for sure so far about PQQ? We know pyrroloquinoline quinone is required in the human diet; without PQQ our biochemical functions would cease to operate properly. In the 2003 Nature article Nutritional biochemistry: A new redox-cofactor vitamin for mammals the researches Takaoki Kasahara and Tadafumi Katopropose proposed that PQQ should join niacin and riboflavin under the umbrella of B vitamins. However, it is now generally accepted that pyrroloquinoline quinone is not a vitamin.

The original claim by Kasahara and Katopropose was likely due to misinterpretation of the data in the Nutritional biochemistry: A new redox-cofactor vitamin for mammals article. It is now generally believed in the academic community that (rather than a vitamin) pyrroloquinoline quinone is better classified as one of a few bio-available compounds that can act as a cell signaling molecule.

Pyrroloquinoline quinone is prevalent in many foods associated with a healthy diet, so people that eat well-rounded meals should get enough to sustain their biological need. It is a water-soluble compound making it difficult to achieve PQQ toxicity. In short, if you would like to take a PQQ supplement — absent of health problems — there should be little concern. Pyrroloquinoline quinone is now being heavily marketed to those concerned with “aging well”. That is despite the fact that to date no published research exists using any type of whole organisms that addresses whether or not methoxatin has an independent or direct influence on aging. All of the work linking pyrroloquinoline quinone to aging is inferential and is based on PQQ’s ability to optimize mitochondrial function.

If you have any questions about pyrroloquinoline quinone, please leave them in the comments section below and I (or my father) will try to answer them as quickly as possible.